Department of Radiation-Oncology, Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, California, USA.
Int J Radiat Oncol Biol Phys. 2013 May 1;86(1):170-6. doi: 10.1016/j.ijrobp.2012.10.040. Epub 2012 Dec 11.
To assess residual setup errors during head and neck radiation therapy and the resulting consequences for the delivered dose for various patient alignment procedures.
Megavoltage cone beam computed tomography (MVCBCT) scans from 11 head and neck patients who underwent intensity modulated radiation therapy were used to assess setup errors. Each MVCBCT scan was registered to its reference planning kVCT, with seven different alignment procedures: automatic alignment and manual registration to 6 separate bony landmarks (sphenoid, left/right maxillary sinuses, mandible, cervical 1 [C1]-C2, and C7-thoracic 1 [T1] vertebrae). Shifts in the different alignments were compared with each other to determine whether there were any statistically significant differences. Then, the dose distribution was recalculated on 3 MVCBCT images per patient for every alignment procedure. The resulting dose-volume histograms for targets and organs at risk (OARs) were compared to those from the planning kVCTs.
The registration procedures produced statistically significant global differences in patient alignment and actual dose distribution, calling for a need for standardization of patient positioning. Vertically, the automatic, sphenoid, and maxillary sinuses alignments mainly generated posterior shifts and resulted in mean increases in maximal dose to OARs of >3% of the planned dose. The suggested choice of C1-C2 as a reference landmark appears valid, combining both OAR sparing and target coverage. Assuming this choice, relevant margins to apply around volumes of interest at the time of planning to take into account for the relative mobility of other regions are discussed.
Use of different alignment procedures for treating head and neck patients produced variations in patient setup and dose distribution. With concern for standardizing practice, C1-C2 reference alignment with relevant margins around planning volumes seems to be a valid option.
评估头颈部放射治疗过程中的残余摆位误差及其对各种患者配准程序下剂量分布的影响。
对 11 例接受调强放疗的头颈部患者的兆伏锥形束 CT（MVCBCT）扫描进行评估，以评估摆位误差。将每个 MVCBCT 扫描与参考千伏 CT（kVCT）进行配准，采用 7 种不同的配准方法：自动配准和手动配准到 6 个单独的骨性解剖标志（蝶骨、左右上颌窦、下颌骨、颈椎 1[C1]-C2 和颈椎 7-胸椎 1[T1]）。比较不同配准方法的位移，以确定是否存在统计学差异。然后，为每位患者的 3 个 MVCBCT 图像上的每种配准方法重新计算剂量分布。将靶区和危及器官（OAR）的剂量-体积直方图与计划 kVCT 的结果进行比较。
配准程序导致患者的配准和实际剂量分布存在统计学显著差异，需要对患者定位进行标准化。在垂直方向上，自动、蝶骨和上颌窦配准主要产生后向移位，导致 OAR 最大剂量增加超过计划剂量的 3%。选择 C1-C2 作为参考标志似乎是有效的，结合了 OAR 保护和靶区覆盖。基于这一选择，讨论了在计划时在感兴趣区域周围应用相关边缘的问题，以考虑其他区域的相对运动性。
对头颈部患者使用不同的配准程序会导致患者摆位和剂量分布的变化。为了标准化治疗实践，C1-C2 参考配准并在计划体积周围应用相关边缘似乎是一个可行的选择。
